A lithium-ion battery in which positive and negative electrodes are stacked or wound through separators is easily increased in capacity per unit battery by an increase in area of each of the positive and negative electrodes or increase in the number of each of the positive and negative electrodes to be stacked, and is thus suitably used as a battery having a large charge/discharge capacity.
In the lithium-ion secondary battery, the positive electrode is manufactured as follows: a positive electrode slurry obtained by mixing a particulate positive electrode active material, a conductive material, a binding agent, and the like is partially applied onto a strip-shaped aluminum foil surface of a collector, followed by drying, and the resultant collector is cut into a block each having a predetermined size. The negative electrode is manufactured in the same way. The procedure is as follows: a negative electrode slurry obtained by mixing a particulate negative electrode active material, a conductive material, a binding agent, and the like is intermittently applied onto a strip-shaped copper foil surface of a collector, followed by drying, and the resultant collector is cut into a block each having a predetermined size.
In the lithium-ion secondary battery, after producing a battery element by laminating a plurality of positive electrodes and a plurality of negative electrodes through separators, electrode tabs each formed integrally with the collector of each electrode or electrode tabs each produced by joining a conductive member to the collector are joined respectively to positive- and negative-electrode lead tabs each having high strength by ultrasonic joining and then accommodated in an outer covering, followed by sealing.
It is known that, in performing the ultrasonic joining for a thin member such as a metal foil, a thin member such as an electrode lead tab is damaged. To cope with this, many approaches are proposed, in which a protective member is interposed between the electrode tab and electrode lead tab, and these members are collectively joined together (see, for example, Patent Document 1).